Can't edit the site due to server error

I am creating a website that is not yet launched through its domain name because the FTP access is not yet available. I can view my information through the MAMP localhost, but I am not longer able to view and edit the site when I go to the localhost:8888 domain through wordpress. This is the error message I receive when I attempt to access my info:

</The website encountered an error while retrieving https://localhost:8888/wp-admin/. It may be down for maintenance or configured incorrectly.>

Has anyone encountered this issue and knows of a solution. I would be extremely thankful and appreciative for any information or getting pointed in the right direction. I am also not sure if I activated or did something wrong…so that could be an issue as well.

Henry